1. Field of the Invention
The present invention relates to a water-based ink. More specifically, the present invention relates to a water-based ink which can be suitably used as a water-based ink for inkjet recording and the like.
2. Discussion of the Related Art
Inkjet recording is a recording system for forming characters or images, comprising directly jetting ink droplets from very fine nozzles to a recording medium, and depositing the ink droplets on the recording medium. This system has some advantages such that not only the device shows excellent operability at a low level of noise, but also the coloration is facilitated and plain paper can be used as a recording medium. Therefore, this system has been widely used. As an ink used for inkjet printers, a pigment-based ink has been used in recent years in order to improve water resistance and light-fastness.
However, there are some defects in the pigment-based ink such that the pigment is less likely to remain on the surface of copy sheets, so that optical density is lowered. Also, when the content of the pigment in the ink is increased in order to improve optical density, there arise some defects such that the ink has a higher viscosity, so that the jetting property of the ink is lowered.
In order to increase the optical density of the pigment-based ink, there have been proposed addition of a polymer containing a polyethylene glycol (meth)acrylate monomer and an α,β-ethylenic unsaturated carboxylic acid (Japanese Patent Laid-Open No. Hei 6-306317), addition of a polymeric dispersant made of a polyethylene glycol (meth)acrylate monomer or a poly(trimethylene glycol) (meth)acrylate monomer (Japanese Patent Laid-Open No. 2000-144031), and the like. Also, in order to improve jetting stability of the pigment-based ink, there have been proposed addition of fine polymer particles (Japanese Patent Laid-Open No. Hei 8-218015, Hei 8-151544 and Hei 8-176488), addition of an ethylene oxide adduct (Japanese Patent Laid-Open No. Hei 8-176481), and the like.
However, there are some defects in the water-insoluble vinyl polymer prepared by polymerizing a (meth)acrylate monomer having an oxyethylene group or an oxytrimethylene group as a nonionic component, such that the water-insoluble vinyl polymer easily penetrates into copy sheets because the polymer itself is highly hydrophilic, thereby lowering optical density when printing, and the defects such that it is difficult to secure stable jetting property because the ink containing the polymer shows high viscosity.
An object of the present invention is to provide a water-based ink which is excellent in water resistance, light-fastness, rubbing resistance, gloss and dispersion stability.
Another object of the present invention is to provide a water-based ink for inkjet recording, which is excellent in jetting stability and capable of giving a printout high optical density.
These and other objects of the present invention will be apparent from the following description.